Centrifugal pump

ABSTRACT

A centrifugal pump having a casing axially divided into two casing halves; an intake and a discharge; as well as an at least one-stage flow channel between the intake and the discharge for a medium to be pressurized; and a shaft mounted for rotation within the casing and being driven by motor; at least one impeller attached thereon and arranged in a stage channel of the flow channel; and at least one guide device on a partition wall arranged within the stage channel in the region of the intake of the associated impeller. There is provided, for influencing the pre-rotation within the flow in the intake of the stage channel of the impeller, that the radial angular position of the guide device arranged on the partition wall is adapted to be adjusted with reference to the plane of partition of the casing as zero position; a positioning device is mounted on the partition wall at a selectable angular distance from the guide device; and said positioning device is received by the casing in the region of the plane of partition of the latter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention in general relates to a centrifugal pump comprising

-   -   a casing axially divided into two casing halves;     -   an intake and a discharge;     -   as well as an at least one-stage flow channel between the intake         and the discharge, for a medium to be pressurized;     -   and a shaft mounted for rotation within the casing and driven by         motor;     -   at least one impeller secured on this shaft and arranged in a         stage channel of the flow channel;     -   and at least one guide means on a partition wall arranged within         the flow channel in the region of the intake of the associated         impeller,         and aims at influencing pre-rotation (swirling).

2. Prior Art

It is known from EP 0 466 350 A2 to provide guide means on partition walls termed as intermediate stage sleeves, said guide means acting as a guide facility within each flow channel or stage channel in the region of the intake of the associated impeller. The guide means are designed to be vane-shaped and to influence the pre-rotation on the intake side of each impeller. The guide means has a fixed position on the partition wall, also called split wall, so that a uniform influence on the pre-rotation results.

When it is desired to change pre-rotation, the present intermediate stage sleeve is substituted by a new sleeve which is provided with a changed guide means with which the desired change of the pre-rotation is brought about, if necessary. The structural expenditure incurred in the development and manufacture of different combinations of partition walls and guide means is extremely high. There is also a considerable disadvantage occurring by having to store different types of partition walls with different guide means, e.g. for a series of centrifugal pumps.

OBJECTS OF THE INVENTION

It is a primary object of the invention to improve the field of applicability of centrifugal pumps of the type outlined in the introductory part of this specification

Furthermore, it is a major object of the present invention to design the intake region of each stage channel such that it becomes possible to influence the pre-rotation in a simple manner.

It is another important object of the invention to facilitate the design and structure of centrifugal pumps of said type.

It is yet a further essential object of the invention to reduce the (overall) costs for the manufacture and maintenance of corresponding centrifugal pumps.

SUMMARY OF THE INVENTION

According to the invention, these objects are achieved in context with the centrifugal pumps of that type

-   -   by the radial angular position of the guide means arranged on         the partition wall being adapted to be adjustable with respect         to the plane of partition of the casing forming the zero         position;     -   by a positioning means being arranged on the partition wall at a         selectable angular distance from the guide means; and     -   by such positioning means being received by the casing in the         region of the plane of partition of the casing.

This solution leads to solving the prior art problems by way of a comparatively simple possibility applicable in a multifunctional manner for influencing the pre-rotation in the flow direction upstream of each impeller of a centrifugal pump. The ability of selecting the simply adjustable radial angular position of the guide means with respect to the plane of partition of the casing forming the zero position is particularly advantageous. The reason for this is that the respectively selected angular position of the guide means on the partition wall defines the extent of the influence on the pre-rotation and thus directly influences the course of the H/Q-characteristic of the pump. If, for example, one starts from a relatively small angle for the selected angular position of the guide means on the partition wall with respect to the zero position and changes the angular position of the guide means on the partition wall such that a relatively large angle results between the zero position and the new angular position, the pre-rotation in the respective pump stages is influenced considerably, so that the H/Q-characteristic of the pump is shifted. This shifting has the consequence that, in particular in the field of larger feed rates, a different course of the H/Q-characteristic of the pump results, which course corresponds to a smaller drop in pressure in the field of larger feed rates.

In the case of multi-stage pumps a uniform angular position of the guide means on the partition wall is expediently selected for one certain pump type. In this manner it becomes possible always to select, in accordance with the invention, the same combination of partition wall and guide means for one structural series of pumps in order to pre-define the influence on the H/Q-characteristic for each type of pump of a certain pump series by selecting correspondingly different radial angular positions of the guide means. Thereby, a pump may be readily adapted to particular requirements by selecting a corresponding angular position of the guide means on the partition wall of each stage channel.

It has proved that the simple ability of adjusting the angular position of the guide means allows for easily adapting a pump to its respective fields of activity and operation, the result thereof being corresponding savings in driving energy.

An essential feature of the invention lies in that a positioning means is mounted on the partition wall at a selectable angular distance from the guide means, which positioning means, when the pump is being assembled, is received within the plane of partition of the casing, or close to the plane of partition, which, regarding the last-mentioned case, means it is received within a groove in the lower casing half. In this manner the guide means may be mounted at very favourable manufacturing conditions without the selection of the radial angular position of the guide means being limited in any way. Quite to the contrary, the same annular body having a portion for the guide means at a constant position may be manufactured for the partition wall. As soon as the required characteristic of the pump is known and the necessary angle between the zero position and the angular position for the guide means has been established therefrom, it is merely necessary to mount the positioning means shifted or displaced by a corresponding angle from the angular position of the guide means, which positioning means is being received in the region of the plane of partition of the casing when assembling the pump. Thereby, the desired combination of a partition wall and a guide means has been completely prepared for insertion into the pump casing. Consequently, for a certain or predetermined series of pumps consisting of types of pumps having different output and performance, by arranging a correspondingly different number of stages, only one certain type of annular body or one certain type of partition wall and one type of guide means is required, which elements are connected to each other or have already been interconnected or are designed to be integral with each other or mutually one-piece shaped. Later on, once the required characteristic of the pump has become known, it is merely necessary to produce the corresponding angular position of the positioning means on the partition wall with respect to the guide means by producing the receptacle required for the positioning means, on the partition wall. By such standardization of the types of partition walls and by the mounting of merely one receptacle for the positioning means on the partition wall before assembling, a considerable reduction of production and storage costs will result. For the operator of the pump it is possible to change the pre-rotation later on by setting up another angular position of the guide means by displacing the positioning means, for example when a change occurs in the parameters of the system.

Preferably, the partition wall is an annular split(ted) wall which limits the stage channel on one side and from which the guide means extends into the stage channel in the axial direction.

Expediently, the guide means has a guide vane directed towards the shaft in an essentially radial direction. Herein, the guide vane advantageously extends into the immediate vicinity of the shaft so that the tip of the guide vane is located at very short distance from the shaft, and thus the flow is almost completely engaged by the guide vane. In this manner, it is possible to influence the pre-rotation in an exceedingly effective manner.

Conveniently, the guide means, moreover, has an arched portion merging into the guide vane which projects from the arched portion in a radial direction. Herein, the lateral faces of the guide vane at both sides of the vane extend in a preferably concavely curved manner on the arched portion. In this manner, the result is a relatively smooth transition of the flow from the wall of the flow channel towards the lateral faces of the guide vane. Herein, it is preferred that on the arched portion the guide vane is disposed in a displaced position, in respect of the length thereof and when seen in its circumferential direction, wherein one of the concavely curved lateral faces of the guide vane is disposed in a longitudinally extended manner and the other one in the manner of a relatively short curvature.

For arranging the guide means in the flow channel it is expedient to provide the arched surface of the arch portion of the guide means in the shape of a circular arc and has essentially the same radius as the circumferential side of the partition wall. Thus, when viewed axially, the arched face lies flush with the circumferential surface of the partition wall so that the result will be that the arched surface of the arched portion may favourably be adapted with respect to the wall of the flow channel.

The free lateral surface of the arched portion, however, advantageously extends essentially within a plane which is perpendicular to the axis of the shaft, while the guide vane has portions which project beyond the plane of the free side surface of the arched portion well into the flow channel.

A partition wall or split wall may be used for the afore-described invention and the embodiments thereof, which wall is moulded in one piece with the guide means. However, it is preferred, according to the invention, that the guide means be designed as a separate structural component and to have an attachment portion by means of which the guide means may be mounted on the partition wall. Separately manufacturing the partition wall and the guide means has, as will yet become clear, many advantages which will not be present in the case of assembling the guide means as a structural component moulded to the partition wall. Consequently, the guide means may be produced as a separate structural component by precision casting, which component may be attached in a preferably detachable manner on the partition wall with its attachment portion which helps facilitating the assembly of the pump. Furthermore, certain advantages will result regarding options of substitution, e.g. if a guide means having other dimensions and parameters is to be substituted for the current one or if the existing guide means may have to be exchanged for other reasons.

According to a preferred further embodiment of the invention, the attachment portion of the guide means is embedded in a cut-out on the circumferential side of the ring-shaped partition wall and is secured therein. Simultaneously, the cut-out on the partition wall and the attachment portion are to be coordinated regarding their shape such that the profile of the circumferential surface of the partition wall is continued without any essential interruption on the surface and on the lateral face of the attachment portion. In these circumstances, it is possible without ado to set and adjust the radial angular position of the partition wall without any structural changes on the partition wall or on its receptacle profile in the casing of the pump, in order to achieve a certain radial angular position of the guide means.

Advantageously, the attachment portion on the partition wall is secured within the partition wall by means of a screw accessible from the circumferential side of the partition wall. In this manner, it is necessary merely to operate one single easily accessible screw in order to secure and to detach the guide means on the partition wall.

Preferably, the attachment of the attachment portion of the guide means is provided in the same axial angular plane as the central plane of the guide vane.

In order to create a positive influence on the flow, it is convenient if two guide means opposing each other diametrically are mounted on the partition wall. According to the requirements of influencing pre-rotation, however, more than two guide means may well be arranged.

Advantageously, a peg may be provided as positioning means, which peg will project outwardly in a radial direction from the circumferential surface of the partition wall or from the ring web thereof, and will engage a receptacle in the region of the partitioning faces of the casing halves. The peg will be preferred as a positioning means because its reception in the chosen angular position of the guide means will require one bore, only, in the circumferential surface of the partition wall, and the reception of the peg in the region of the partitioning faces of the casing halves will also require merely one groove in the lower casing half, which groove will be engaged by the peg when assembling the pump. It is a further advantage of this embodiment according to the invention that the peg simultaneously will prevent any distorting of the partition wall or the split wall in the casing once it has been received in the receptacle or the groove in the lower casing half.

With the above in view, the gist of the present invention as well as further objects and important features of construction and combination of parts will become apparent from the following description of an example of preferred embodiment of the invention and is to be seen in connection with the appending claims. Such preferred embodiment of a centrifugal pump will be explained hereinafter with reference to the accompanying drawings.

Also, simultaneously avoiding repetition, reference is made to yet further advantages of the invention as have been mentioned in the foregoing part of the specification, which advantages apply to the following description and, in particular, to the drawing showing an example of the preferred embodiment, as well as to the appending claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, there is shown in:

FIG. 1 a representation of a vertical section of a centrifugal pump having a horizontal partition as well as fourteen pump stages;

FIG. 2 a representation of a vertical section of a portion of the centrifugal pump of FIG. 1, wherein the portion in FIG. 1 has been shown to be situated between the pairs of section lines II-II and has been represented on a larger scale in FIG. 2;

FIG. 3 a sectional representation of the centrifugal pump of FIG. 1 and FIG. 2 along the section line III-III of FIG. 1 and FIG. 2;

FIG. 4 a perspective view of a split wall having two guide means which are attached in a diametric position on the split wall;

FIG. 5 a frontal view of the split wall of FIG. 4;

FIG. 6 a sectional view of the split wall of FIGS. 4 and 5 along the sectional line A-A of FIG. 5;

FIG. 7 a sectional view of the split wall of FIGS. 4 to 6 along the section line B-B of FIG. 5;

FIG. 8 a perspective view of one of the guide means of FIG. 4;

FIG. 9 a view of the guide means of FIG. 8 when viewed from one side;

FIG. 10 a view of the guide means of FIG. 8 when viewed from the side other than in FIG. 9;

FIG. 11 a sectional view of the guide means of FIGS. 8 to 10 along the section line A-A of FIG. 10;

FIG. 12 an H/Q-diagram representing the characteristics of a centrifugal pump without guide means, on the one hand, as well as with guide means by way of two different embodiments, on the other, wherein the first and the second embodiment are clearly different from one another by different angular positions of the guide means.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 by way of a vertical sectional representation of a centrifugal pump, the latter comprises a casing generally designated 1 and including two casing halves 2, 3 arranged on both sides of a horizontal plane of partition 4. These halves 2, 3 are attached to each other in a known manner. A continuous shaft 5 extends through the casing 1, which shaft, as has been shown, is radially mounted for rotation on each side of the casing 1 in one mount 6, 7, each, is secured against axial displacement in known manner, and, on one side, has a shaft end 8 for connection to a shaft drive.

As may be taken from the drawing, in this example of embodiment the centrifugal pump includes fourteen stages altogether for pressurizing a fluid medium such as oil or water, of which stages seven form a spiral-shaped flow channel starting from a merely provisionally indicated intake 11, from which the pressurized fluid is made to arrive at the beginning of the second compression stage array via common reverse-flow channels 13, 14, said second array also comprising seven stages, wherein the fluid is further pressurized in a flow which proceeds spiral-shaped as well, however in a direction counter the first-mentioned flow, and is conveyed to a provisionally plotted discharge 12 of the centrifugal pump.

Each stage is associated with an impeller 9 secured to the shaft 5 radially as well as axially and is arranged in one of the fourteen stage channels 10 as can be taken particularly clearly from FIG. 2 due to the enlarged representation therein. A guide means 15 for influencing the pre-rotation of each impeller 9 is connected upstream of each stage channel, however with the exception of each first stage of each compression stage array, special attention being drawn to the representation in the section plane of the representation of FIG. 2, particularly due to the enlarged scale. FIG. 3, as well, adds to the comprehension of the shape and position of the guide means 15 which is respectively attached to a split wall 16 associated with the respective stage as will be explained in greater detail later on. The representation of FIG. 3 shows, as well as FIG. 2, two guide means 15 opposing each other diametrically on the split wall 16 associated with the respective stage. The split wall 16 is secured axially within the casing 1 by means of an annular web 17 in an annular groove 18 formed in one of the casing halves 2, 3, while the ring-shaped split wall or the partition wall 16 is fitted into an inner surface 20 of the casing wall 21 of each stage, which inner surface is designed to have a corresponding annular shape. In order to visualize the angular adjustability of the guide means 15 with respect to the plane of partition 4 a second pair of guide means is represented in FIG. 3 under a position angle which is smaller than the guide means 15 arranged in the sectional plane.

In FIG. 4 one of the annular-shaped partition walls 16 having the two guide means 15 opposing each other diametrically is shown, which walls 16 are inserted into the lower casing half 2 when assembling the casing 1 before the latter is closed by fitting the casing half 3 on the casing half 2. The partition wall 16 is explained in the following by way of FIGS. 5 to 7 and, following that, the guide means 15 is explained in greater detail by means of FIGS. 8 to 11, which elements, together, form the combination to be taken from FIG. 4.

For receiving the guide means 15, two cut-outs 22 which are approximately rectangular when seen in cross-section and oppose each diametrically are provided in the partition wall 16 on the circumferential side 19 and of the annular web 17. One threaded hole 23, each, for receiving a bolt 24 (FIG. 4) is arranged on the bottom of each cut-out 22 in a position as can be taken from FIGS. 5 to 7.

Once the positioning angle for the guide means 15 has been selected starting from the plane of partition 4 of the casing 1, which angle is 55° in the present case, a bore 25 for receiving a positioning means 26 which, in the present case, has the shape of a peg 27 (viz. FIG. 4) is inserted through the ring web 17 of the partition wall 16 into the latter. In FIG. 6 the bore 25 has been represented shifted into the sectional plane in order to clarify the position of the bore 25 on the annular web 17. In the left portion of FIG. 5, it has been represented schematically that a groove 43 is arranged in the region of the plane of partition 4, i.e. closely below the same and in the lower casing half 3, in which groove 43 the peg 27 is received when assembling the casing 1 in order to define the positioning angle of 55° of the cut-out 22 for the guide means 15. In the present case, the guide means 15 for the stages 2 to 7 of the first array of stages of the pump are arranged in this manner. For the stages 9 to 14 having an opposing flow, the partition wall 16 represented in FIGS. 5 to 7 is used in a mirror-inverted arrangement. To this end, the bore 25 has already been provided in the right-hand portion of FIG. 5 in the annular body of the partition wall 16, which bore is formed in a corresponding, actually not shown groove of the lower casing half 3 closely below the plane of partition currently designated by 4′. It goes without saying that the partition wall 16 for application in the stages 9 to 14 is turned correspondingly into the area of the plane of partition 4.

The guide means 15 which can be taken in particular from FIG. 4 and has been represented as a separate component in FIGS. 8 to 11 has an attachment portion 28 and an arched portion 29 preferably produced by precision casting integrally with the attachment portion, as can be taken from FIG. 4 as well as 8 to 11.

The cut-out 22 in the partition wall 16 and the attachment portion 28 are adapted to each other with regard to their shape and position such that the profile of the circumferential side 19 of the partition wall 16 is continued on the surface 31 and on the side face 32 of the attachment portion 28 essentially without interruption. In this manner, the partition wall 16 together with the ring web 17 can be inserted in a practically random angular position into the annular groove 18 formed in the casing halves 2, 3, i.e. independent of the angular position predetermined for the guide means 15.

In the attachment portion 28, there are arranged, in a position and design as may be taken from the drawing, a first bore 33 for receiving the head of the bolt 24 mentioned in context with FIG. 4, and a second bore 34 which is coaxial with the first bore 33, for receiving the shank of the bolt 24 with a shoulder 35 arranged between the bores 33, 34. Herein, the first bore 33 partly traverses a web 36 on the surface 31, which web is in continuation of the annular web 17 of the partition wall 16.

A guide vane 30 defining a central plane 30 a radially extends inwardly (cf. FIGS. 3 and 4) from the arched portion 29 restricted by an arched face 29 a, which is in the shape of a circular arc and tapers out in a rounded tip 37 which, in the assembled position of the guide means 15 (cf. FIG. 2) is arranged immediately besides the shaft 5. A lateral face 38 of the guide vane extends concavely curved as well as in a relatively strongly stretched manner, whereas another lateral face 39 on the other side of the guide vane 30 extends as a relatively short concave curve. A free lateral face 40 of the arched portion 29 extends essentially in a plane which is perpendicular with respect to the axis of the shaft 5. In relation thereto, the guide vane 30 has portions 41, 42 (cf. FIG. 11) which protrude beyond the plane of the free lateral face 40 of the arched portion 29, as can already be taken from FIG. 2 and also from FIG. 8.

In order to achieve a desired influence on the pre-rotation for each stage channel 10 in which a guide means 15 may be arranged, a uniform angular position of the guide means 15 is defined for a certain centrifugal pump array, and, depending on this angular position, the positioning means 26, which in the present case is the peg 27, is mounted. The partition walls 16 may moreover be mounted in a completed manner with the corresponding cut-outs 22. When assembling the pump, the partition walls 16 are mounted on the shaft 5, preferably together with the lower guide means 15 fixed thereto, in the lower casing half 2, and subsequently the upper guide means 15 as well, their attachment portions 28 are attached to the partition walls 16 by means of the bolts 24, the result being the combination of the components as can be taken from FIG. 4 within the casing 1. Incidentally, the sequence of the steps of assembling depends on the respective circumstances.

The diagram shown in FIG. 12 communicates how the pre-rotation of the flow of the fluid to be pressurized is influenced in the inlet region of the impeller of each pump stage provided with a guide means. Herein, the shown characteristics are only to be understood as to their tendency of influencing the pre-rotation. The characteristics refer to a fourteen-stage centrifugal pump having approximately the structure as may be taken from FIG. 1. In this context, the stages 2 to 7 as well as 9 to 14 are equipped with guide means 15. Characteristic a shows the results for a pump achieved without any guide means. Characteristic b is achieved with guide means in this pump at a relatively large angle of position. If one chooses a smaller angle of position for the guide means for this pump, a course of the characteristic of this pump results as has been designated by c. From such comparison of characteristics it follows that a relatively high loss in pressure of the pump may be prevented in the case of large flow rates if the angle of position of the guide means is selected to be relatively large.

In order to provide a pump having guide means shifted to a second angular position in respect of a first angular position there is, according to the invention, no requirement at all to manufacture, as had to be done previously, new split walls having correspondingly shifted guide means, but for changing the angular position of the guide means it is only necessary to dislocate the positioning means 26, i.e. the peg 27 in the example of embodiment of FIG. 4 or the pegs 27 which principally define the 0° position by their arrangement in the plane of partition 4 of the pump, on the circumferential side 19 or on the ring web 17 by a corresponding angle so that the desired changed angular position for the guide means 15 will result in respect of the plane of partition 4 of the pump. 

1. A centrifugal pump comprising: casing means axially divided into two casing halves; intake means and discharge means; at least one-stage flow channel defined between said intake means and said discharge means for receiving a medium to be pressurized; shaft means mounted for rotation within said casing means and being driven by motor, at least one impeller means attached on said shaft means and arranged in a stage channel means of said flow channel; partition wall means arranged within said stage channel means in a region of said intake of an associated one of said impeller means; at least one guide means disposed on said partition wall means; a radial angular position of said guide means disposed on said partition wall means being adapted for adjustment with reference to a plane of partition of said casing means at a zero position; positioning means being provided and mounted on said partition wall means at a selectable angular distance from said guide means; and said positioning means being received by said casing means in a region of a plane of partition defined by said two casing halves.
 2. The centrifugal pump as claimed in claim 1, wherein said partition wall means is an annular split wall restricting said stage channel means on one side, from which annular split wall said guide means extends into said stage channel means in an axial direction.
 3. The centrifugal pump as claimed in claim 1, wherein said guide means comprises guide vane means adapted to extend in an essentially radial direction towards said shaft means.
 4. The centrifugal pump as claimed in claim 2, wherein said guide means comprises guide vane means adapted to extend in an essentially radial direction towards said shaft means.
 5. The centrifugal pump as claimed in claim 3, wherein said guide vane means is provided with a tip end and extends into an immediate vicinity of said shaft means so that said tip end of said guide vane means is disposed at a very short distance from said shaft means.
 6. The centrifugal pump as claimed in claim 4, wherein said guide vane means is provided with a tip end and extends into an immediate vicinity of said shaft means so that said tip end of said guide vane means is disposed at a very short distance from said shaft means.
 7. The centrifugal pump as claimed in claim 3, wherein said guide means includes an arched portion adapted to merge into said guide vane means protruding from said arched portion in a radial direction.
 8. The centrifugal pump as claimed in claim 4, wherein said guide means includes an arched portion adapted to merge into said guide vane means protruding from said arched portion in a radial direction.
 9. The centrifugal pump as claimed in claim 5, wherein said guide means includes an arched portion adapted to merge into said guide vane means protruding from said arched portion in a radial direction.
 10. The centrifugal pump as claimed in claim 6, wherein said guide means includes an arched portion adapted to merge into said guide vane means protruding from said arched portion in a radial direction.
 11. The centrifugal pump as claimed in claim 7, wherein said guide vane means defines lateral faces extending in concave curving at both sides of said guide vane means on said arched portion.
 12. The centrifugal pump as claimed in claim 8, wherein said guide vane means defines lateral faces extending in concave curving at both sides of said guide vane means on said arched portion.
 13. The centrifugal pump as claimed in claim 9, wherein said guide vane means defines lateral faces extending in concave curving at both sides of said guide vane means on said arched portion.
 14. The centrifugal pump as claimed in claim 10, wherein said guide vane means defines lateral faces extending in concave curving at both sides of said guide vane means on said arched portion.
 15. The centrifugal pump as claimed in claim 11, wherein said guide vane means is disposed on said arched portion in a position which is displaced in relation to a length of said arched portion and when viewed in a circumferential direction thereof, and wherein one of said concavely curved lateral faces of said guide vane means extends in a longitudinally stretched manner, whereas an other one of said concavely curved lateral faces extends as a relatively short curving.
 16. The centrifugal pump as claimed in claim 12, wherein said guide vane means is disposed on said arched portion in a position which is displaced in relation to the length of said arched portion and when viewed in a circumferential direction thereof, and wherein one of said concavely curved lateral faces of said guide vane means extends in a longitudinally stretched manner, whereas an other one of said concavely curved lateral faces extends as a relatively short curving.
 17. The centrifugal pump as claimed in claim 7, wherein the guide vane means is designed with portions which protrude beyond a plane of a free lateral surface defined by said arched portion.
 18. The centrifugal pump as claimed in claim 8, wherein the guide vane means is designed with portions which protrude beyond a plane of a free lateral surface defined by said arched portion.
 19. The centrifugal pump as claimed in claim 1, wherein said guide means is designed as separate structural component means and comprises attachment portion means adapted to mount said guide means on said partition wall means.
 20. The centrifugal pump as claimed in claim 19, wherein said attachment portion means of said guide means is adapted for insertion in cut-out means provided on a circumferential face of said partition wall means and is designed in annular shape, for being secured thereto.
 21. The centrifugal pump as claimed in claim 20, wherein said cut-out means on said partition wall means, and said attachment portion means are adapted to each other regarding their shape such that a profile of said circumferential face of said partition wall means continues essentially without interruption on a surface and on a lateral face defined on said attachment portion means.
 22. The centrifugal pump as claimed in claim 1, wherein said positioning means comprises a peg protruding outwardly from said circumferential face of said partition wall means in a radial direction and engaging receptacle means defined in a region of separation faces of said two casing halves.
 23. The centrifugal pump as claimed in claim 1, wherein said positioning means comprises a peg protruding outwardly from annular web means in a radial direction and engaging receptacle means defined in a region of separation faces of said two casing halves. 